The GP100 is probably the best value 357 Magnum out there.
I would personally get stainless, Rugers "bluing' isn't great....it's not even good.
I have a 4.2" GP100 and I've had a 6" version. The only reason I went with a 4.2" is because I have a 6.5" Super Redhawk .44 so I wanted something a little different. The 4.2" balances well and I like it. Also, there is a 5" version out there too, shouldn't be too hard to find, I know Buds has them in stock. The Match Champion is nice too, but personally I don't like the look of half lug barrels (at least on a GP100), seems too 1970's for me. Put a Wolff reduced power springs in it and it's a pretty darn decent trigger, which is probably my biggest complaint on the gun from the factory, the trigger isn't very clean feeling at all, a bit gritty.
I put a green fiber optic front sight on mine, it's so easy to do it's crazy plus it lights up like crazy outside. Since you said it's mainly for range use, I'd personally lean more towards the 6" version.
Can't go wrong with a GP100, but I'd highly recommend getting stainless and a Wolff reduced power spring kit for it.